There are many prosthetic devices for implantation in human or animal bones. One of the more commonly used types includes a solid member which is cemented directly into a cavity in the bone. An example of this is a prosthetic device used to replace the head of a human femur. The device is generally a solid stainless steel or titanium steel curved shaft mounting a ball at one end.
A cavity is prepared in the bone as for example reaming the medullary canal in the human femur. A cement such as polymethylmethacrylate, also known as PMMA, is poured into the cavity and the prosthetic device inserted. The cement hardens within a few minutes. However, the hardening process is exothermic and the evolved heat kills the bone cells adjacent the implant. When the cells grow back, they form a fibrous layer which encapsulates the prosthesis. This layer is hard and after its formation provides poor damping properties when impact is imparted to the prosthetic device.
It has been found that the device tends to jar loose and the cement-bone interface in time breaks down. The implant then must be replaced on an average of every 5 to 10 years, and when this occurs, the old cement must be completely removed from the cavity. This tends to weaken the original bone because the fibrous bone layer must also be removed.
It is one of the objects of this invention to provide a prosthetic device which in the implantation process does not require an exothermic cement.
Another object of this invention is to provide a prosthetic device which need not be completely removed if a portion of it requires replacement or repair.